From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753070AbaHKMMr (ORCPT ); Mon, 11 Aug 2014 08:12:47 -0400 Received: from cantor2.suse.de ([195.135.220.15]:38356 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751638AbaHKMMq (ORCPT ); Mon, 11 Aug 2014 08:12:46 -0400 Date: Mon, 11 Aug 2014 13:12:42 +0100 From: Mel Gorman To: Vlastimil Babka Cc: Andrew Morton , Linux Kernel , Linux-MM , Linux-FSDevel , Johannes Weiner Subject: Re: [PATCH 6/6] mm: page_alloc: Reduce cost of the fair zone allocation policy Message-ID: <20140811121241.GD7970@suse.de> References: <1404893588-21371-1-git-send-email-mgorman@suse.de> <1404893588-21371-7-git-send-email-mgorman@suse.de> <53E4EC53.1050904@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <53E4EC53.1050904@suse.cz> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Aug 08, 2014 at 05:27:15PM +0200, Vlastimil Babka wrote: > On 07/09/2014 10:13 AM, Mel Gorman wrote: > > --- a/mm/page_alloc.c > > +++ b/mm/page_alloc.c > > @@ -1604,6 +1604,9 @@ again: > > } > > > > __mod_zone_page_state(zone, NR_ALLOC_BATCH, -(1 << order)); > > This can underflow zero, right? > Yes, because of per-cpu accounting drift. > > + if (zone_page_state(zone, NR_ALLOC_BATCH) == 0 && > > AFAICS, zone_page_state will correct negative values to zero only for > CONFIG_SMP. Won't this check be broken on !CONFIG_SMP? > On !CONFIG_SMP how can there be per-cpu accounting drift that would make that counter negative? -- Mel Gorman SUSE Labs